diff --git a/webdev/CHANGELOG.md b/webdev/CHANGELOG.md
index abc66c2be..fefe68694 100644
--- a/webdev/CHANGELOG.md
+++ b/webdev/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.2.1
+
+- Exit with an error if unsupported arguments are passed to `build` command.
+
 ## 0.2.0
 
 - Pass the arguments supporting `directory:port` for the `serve` command.
diff --git a/webdev/lib/src/command/build_command.dart b/webdev/lib/src/command/build_command.dart
index 1d1c64fdd..f2a935c99 100644
--- a/webdev/lib/src/command/build_command.dart
+++ b/webdev/lib/src/command/build_command.dart
@@ -3,6 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+
+import 'package:args/command_runner.dart';
+
 import 'command_base.dart';
 
 /// Command to execute pub run build_runner build.
@@ -16,5 +19,13 @@ class BuildCommand extends CommandBase {
   final description = 'Run builders to build a package.';
 
   @override
-  Future<int> run() => runCore('build');
+  Future<int> run() {
+    if (argResults.rest.isNotEmpty) {
+      throw new UsageException(
+          'Arguments were provided that are not supported: '
+          '"${argResults.rest.join(' ')}".',
+          argParser.usage);
+    }
+    return runCore('build');
+  }
 }
diff --git a/webdev/pubspec.yaml b/webdev/pubspec.yaml
index a06406bbd..526c09bf2 100644
--- a/webdev/pubspec.yaml
+++ b/webdev/pubspec.yaml
@@ -1,5 +1,5 @@
 name: webdev
-version: 0.2.0
+version: 0.2.1-dev
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/webdev
 description: >-
diff --git a/webdev/test/integration_test.dart b/webdev/test/integration_test.dart
index 2ec64c6e0..70f195671 100644
--- a/webdev/test/integration_test.dart
+++ b/webdev/test/integration_test.dart
@@ -19,6 +19,15 @@ void main() {
     await process.shouldExit(64);
   });
 
+  test('passing extra args to build fails with bad usage', () async {
+    var process = await runWebDev(['build', 'extra', 'args']);
+
+    await expectLater(process.stdout,
+        emits('Arguments were provided that are not supported: "extra args".'));
+
+    await process.shouldExit(64);
+  });
+
   var invalidRanges = <String, List<String>>{
     'build_runner': ['0.7.13+1', '0.9.0'],
     'build_web_compilers': ['0.3.5', '0.4.0']